Dairy wastewater tertiary treatment using a horizontal sub-surface flow wetland

MAINE, M.A.; GRIFFA, C.; PANIGATTI, M.C.; SCHIERANO, M.C.; BOGLIONE, R.

AARHUS

Simposio; 8th International Symposium on Wetland Pollutant Dynamics and Control-WETPOL; 2019

AARHUS UNIVERSITY

As a result of their operation, Argentinian dairy companies generate a large volume of effluents. Although wastewaters are treated through different methods, they often exceed discharge limits established by current regulations. Therefore, after biological treatment, a polishing wastewater treatment is required. The aim of this work was to evaluate the efficiency of a horizontal sub-surface wetland (HSSW) for the final treatment of a dairy wastewater. Effluent is treated by a sequence of 12 aerobic ponds (biological treatment). A fiberglass pilot scale HSSW was located after the ponds. Its dimensions were 0.95 m width, 2.5 m length and 0.70 m depth. River gravel was used as substrate and Typha domingensis was planted. Wetland feeding was carried out using a pump. Hydraulic residence time was 7 days. In order to evaluate contaminant removal efficiencies, pH, electrical conductivity (EC), suspended solids (SS), total Kjeldahl nitrogen (TKN), ammonium (NH4+), nitrate (NO3-), nitrite (NO2-), total phosphorus (TP), chemical oxygen demand (COD) and biological oxygen demand (BOD) were analyzed in the effluent before and after treatment during 3 months. Mean concentrations of different parameters measured at the inlet wastewater were: pH: 9.08+0.11; EC: 5.33+0.34 (mS cm-1); SS: 172+47 (mg l-1); COD: 345+49 (mg l-1); BOD: 88+25 (mg l-1); TKN: 44.3+7.0 (mg l-1N); NH4+: 8.4+1.5 (mg l-1N); NO3-: 15.9+11.1 (mg l-1 N); NO2-: 28.7+4.5 (mg l-1N); TP: 44.4+11.1 (mg l-1 P). pH showed significant differences before and after treatment, presenting a mean value of 9.08 and 8.40, respectively. Electrical conductivity decreased significantly from 5.33 to 4.70 mS.cm-1 after the treatment. High removal efficiencies were obtained for SS (86.3+5.3 %), COD (74.7+5.5 %), and BOD (64.3+6.7 %). Nitrate and nitrite showed satisfactory removals of 56.3+11.6% and 99.9+0.2%, respectively. These performances are in agreement with those reported in literature for HSSWs. Ammonium concentrations in the effluent were higher before than after the treatment (8.4 +1.5 mg l-1 and 22.2+9.2 mg l-1, respectively). Nevertheless, mean ammonium concentrations at the outlet remained under legislation limit. TKN removal efficiency was low and presented a high variability (16.1+10.3%), probably due to mineralization of proteins but low nitrification of ammonium. TP concentration decreased satisfactorily, with a mean removal percentage of 51.4+16.4%. Removal efficiencies of TP in HSSW with commonly used substrates like river gravel are usually low.Studied HSSW planted with T. domingensis was efficient for the final treatment of dairy wastewater, reaching high removals of SS, COD, BOD, TP, nitrate and nitrite. The quality of the effluent was significantly improved, complying with state regulations for its discharge to the environment.